code: def channels(melspec_sr):
      S, _ = melspec_sr
      return np.linspace(0, S.shape[0], num=5, dtype=int)
  
imports: import pytest
  from contextlib import nullcontext
  import os
  import warnings
  import numpy
  import librosa
  from test_core import srand
label_desc: Use image node_id 9 for calling a global function with example usage: channels(melspec_sr) and returns: np